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Desktop CNC machinery typically uses stepper motors, often because they result
in lower system cost, since they don’t require a position feedback sensor.
But there are some situations where having a position feedback sensor is
desirable or necessary, and the power output of a stepper motor,
specially at high speeds, becomes the bottleneck for those who want a better
performing machine.

I wanted to build a desktop CNC mill that was as impressive as some big name
industrial machines. I decided to use brushed motors, as good quality and
performance, reasonably priced units are easy to find and come in a wide variety
of mechanical and electrical configurations. Speeds in excess of 15 m/min or 600
inches per minute and pushing through metal are no problem for a brushed
servomotor coupled to a ballscrew, and the position feedback lowers the risk of
ruining a machine job.

But it was difficult to find a commercially available, low cost motor controller,
as they often have features one does not really need, or they’re built
to handle large motors. That’s why I decided to create what would become
the Tarocco motor controller.

Who Should Buy Tarocco?

You should consider buying this controller if you:

Need a low cost, step/direction compatible brushed motor controller

Want to improve the performance of an existing CNC machine

Are automating a manual machine like a mill or a lathe

Need a reliable brushed motor controller for mobile robotics

Have some brushed motors that you want to put to good use

Use linear actuators in a precise and controlled manner

Need a good quality, hackable H bridge

Want to support an open source project

Tarocco allows the use of brushed motors with CNC machine controllers that
communicate using the popular step and direction signal interface. As the
controller receives step pulses at certain frequency, it will try to spin the
motor immediately while reading the encoder signal, ensuring the number and
frequency of encoder pulses correspond to the step signal. It essentially allows
to drive a brushed motor as a stepper motor of not just, 800, 1600, or even 3200 steps per revolution,
but the resolution of the quadrature encoder you use, which can be any value you need.
If the controller, for some reason, cannot make the motor reach the desired position, it will
signal the other controllers in the system, allowing them to stop their
respective motors in time to avoid messing up the printing or cutting job.

The controller can deliver up to 360 W (36 V 10 A) continuously to a motor,
making it a good choice for machines that need to accelerate bigger loads or
where high speed motion is required. It also features a current limiting
function, useful for protecting the motor from overheating and for controlling
the amount of torque exerted on the machine.

With practically the same amount of money that gets you only one of the other controllers, you can buy enough Tarocco boards for a 3-axis machine!

Manufacturing Plan

As soon as the campaign ends, the electronic components will be purchased and
sent to the PCB assembler. Six weeks from the end of the campaign, including non-
working days we expect to have the complete batch of boards and motors ready
for shipping.

Risks & Challenges

Several Barocco boards have been assembled and tested on machines that do real
work. The main risk is that the parts get delayed in shipment.

Tarocco will be provided with the base firmware that allows it to perform its
duties as a motor controller for CNC machines. However, firmware updates will be
released in the future to increase the performance of the controller. New
firmware images will be made available, to cover a broader range of use cases
for the board, like making it compatible with RC gear, or to provide different
ways to communicate with the board, thus taking advantage of the highly
configurable architecture of the PSoC4 microcontroller.